In the service area or feeder nets of communications systems or networks, different transmission procedures are used to transmit data. For example, digitized voice information or Internet data information via lines may be transmitted via 2-wire or 4-wire lines. Frequently used transmission procedures include the baseband transmission procedure and single-carrier or multi-carrier procedures. Additional echo compensation processes are required for bi-directional data transmission via two-wire lines. Modems frequently use single- or multiple carrier frequency processes, whereby appropriate modulation procedures—in particular phase modulation procedures—depending on the transmission rates to be achieved, are applied.
Modems use a default transmission rate that is reduced during temporary interference, which causes a sharp drop in transmission quality. Once the interference is eliminated or repaired, the modem returns to the original transmission rate.